Ground rules are rules or algorithms applied to the design data for a semiconductor chip in the design phase. In the design phase, the designers follow the design rule during a logic synthesis step and a placement and routing step. A design rule checking program, which is typically released to designers as part of a technology platform, provides an automated method of checking the design data for any violations of the ground rules. Thus, the design rules serve as a systematic mechanism to insure that a semiconductor chip design is compatible with capabilities of manufacturing processes employed in the semiconductor technology. Conformity of a given design data to the design rules improves the probability of obtaining a reasonable yield from physical semiconductor chips, that is, semiconductor chips manufactured in a semiconductor chip fabrication facility, that conforms to the ground rules of the semiconductor technology. Practically, barring any systematic or logical errors in the design data, a high degree of conformity to the ground rules correlate to a high yield in manufacturing.
Despite the benefits that the ground rules provide in terms of yield management, the ground rules pose limitations between the various elements of the design data during the design phase. Of particular concern is the limitation on the shapes in a design level due to the constraint of a minimum overlap with another level, which is typically a level directly above or directly below. For example, a metal line contacting a via therebelow or a via thereabove needs to have a certain minimum overlap to insure that sufficient electrical contact is present between the metal line and the via. Likewise, a minimum overlap is sometimes required between a structure in a polysilicon conductor (PC) level and another structure in a recessed oxide (RX) level.
Typically, a complex set of ground rules are provided to insure that such structures meet or exceed a minimum level of overlap. For example, metal lines, vias, or other shaped in relevant levels are required to have one of predefined widths, lengths, or other geometric limitations. In many cases, such ground rules are provided as a complex set of logical instructions including alternatives and/or combinations, making understanding of such ground rules by designers time-consuming and/or challenging. Also, such ground rules tend to limit choices for the designers and reduce the flexibility in the design of semiconductor devices rather severely.
In addition, the ground rules are also set up such that semiconductor devices meet a certain level of performance criteria even in the worst combination of relevant ground rules. By construction, therefore, the ground rules insure that a model calculation of model parameters would satisfy a minimum performance specification such as electrical resistance of a contact between a line and a via, electromigration resistance of a contact between a line and a via, and/or expected yield of a particular contact structure or an overlap structure. A downside of such an approach is that many designs are unintentionally over-engineered, i.e., provides more than sufficient performance when the elements of the design data are not configured to provide worst combinations. Such over-engineering may result in a significant increase in the area that the designs take up compared to an optimally design, which would violate some of the ground rules but would still deliver sufficiently satisfactory performance.
In view of the above, there exists a need for a method of providing a design data that meets performance specification without resorting to ground rules comprising a complex set of logical instructions. Specifically, there exists a need for simplified ground rules that are less restrictive to the design data.
Further, there exists a need for enabling a model calculation for such a design data based on such simplified ground rules. In addition, there exists a need for a semiconductor design methodology employing such ground rules to check and/or improve a semiconductor device design.